Nov. 05--As federal investigators ruled out mechanical defects Friday as the cause of a school bus crash that killed six adults in Southwest Baltimore this week, it came to light that the driver had been on medication for seizures in the past.

Police have said they were exploring whether the driver, 67-year-old Glenn Chappell, suffered a medical emergency when he was driving Tuesday morning on Frederick Avenue and rear-ended a Ford Mustang before veering into oncoming traffic and crashing into a Maryland Transit Administration bus.

Chappell, the MTA driver and four passengers on the MTA bus died in the crash. Eleven people were injured.

"I'm not at liberty to discuss any of his potential medical history, but that certainly will be part of our investigation," police spokesman T.J. Smith said.

Chappell's driving and medical history have been under scrutiny. While school district officials say he recently passed a physical, Chappell failed to submit documentation to the Maryland Motor Vehicle Administration showing he was in good health. As a result, he lost his commercial driving privileges.

In 2014 in Ellicott City, Chappell was driving a Buick LeSabre and crossed a median into oncoming traffic, hitting a guardrail, another median and trees, according to a Howard County police accident report. His wife told police at the time that he was taking medications for seizures.

Police said Chappell was "believed to have suffered a medical condition" and could not explain to officers what happened.

The severity of this week's crash in Irvington has brought federal investigators to Baltimore. The National Transportation Safety Board is investigating, along with Baltimore police.

Police have said they found no indication Chappell applied the school bus brakes before the collision, and they have no reason to suspect that Chappell intentionally rammed the MTA bus. The school bus, police said, was speeding.

Investigators said they intend to ask a school bus aide -- who was the only other person on the school bus -- what happened just before the crash. Police said they are trying to schedule a time to talk with the aide's lawyer.

The school bus, owned by AAAfordable Transportation Inc., passed an inspection in April, according to Baltimore school district officials. Chappell worked for AAAfordable, a contractor with the district. On Friday, federal officials said they had examined both buses.

"We have completed the mechanical inspections of both buses involved in the crash, and no mechanical defects or deficiencies were noted," said Jennifer Morrison, an investigator with the National Transportation Safety Board.

Police also identified Friday the sixth person killed in the crash as Pattie Lynn Martinez, 46. She was homeless but was known to live last in Fells Point, police said.

In addition, police announced that an 11th person -- a 28-year-old woman -- was injured in the crash, and that she remains hospitalized. Police are not naming victims who survived.

Smith said that in the "chaos" of the accident scene, police weren't aware that she had been transported to the hospital.

The state Motor Vehicle Administration revoked Chappell's commercial driving privileges two months ago because he failed to provide the agency with the necessary health certificate, state officials said.

Baltimore schools, however, showed The Baltimore Sun a medical examiner's certificate that declared Chappell was a qualified to drive. The certificate was dated June 20, 2016, and was valid for one year. An attorney for AAAfordable, George Bogris, said the company also had a current certificate for Chappell.

Baltimore City Councilwoman Mary Pat Clarke called Friday on the city school system to end its six-year contract with AAAfordable.

"It's the only thing to restore confidence for a lot of families," she said.

Clarke questioned whether Chappell should have been driving. "I don't know how he got through the screening," she said.

Morrison said it was the first crash involving a transit bus that the National Transportation Safety Board has investigated since 1997. Agents closed one lane of Frederick Avenue on Friday to measure the road and determine the precise speed of the school bus.

Federal investigators and Baltimore police have obtained four surveillance videos that show the school bus on its approach to the crash site, Morrison said, but none shows the collision.

Investigators also are recovering data from control modules in the engine and air bags. Such modules can capture several seconds' worth of data, such as engine revolutions, speed, how much throttle was applied, whether brakes were engaged, any change in velocity, and if a seat belt was fastened.

A preliminary report from the National Transportation Safety Board is expected within two to three weeks. The findings could help authorities improve transportation safety in Baltimore and beyond, Morrison said.

Smith, the police spokesman, said authorities have received conflicting information regarding Chappell's health certification and whether he was legally permitted to drive a school bus.

Chappell has had other legal problems stemming from his driving in the past.

Chappell was sued in Baltimore for $30,000 over a 2007 crash in which another driver said Chappell tried to make a left-hand turn in front of him. The case was settled in 2010; terms were not disclosed in court papers.

He lost a civil case over hitting a parked car in Baltimore in 2008. Nationwide Insurance said in its complaint that Chappell's vehicle "veered from the roadway" and struck the car. The court ordered Chappell to pay about $2,400.

He pleaded guilty in 2014 to failing to show a registration card on demand and in 2015 to driving a vehicle with a suspended registration.

Howard County sued Chappell over $150 in unpaid traffic tickets from 2014, court records show, but officials were unable to find him to serve legal papers. The lawsuit stemmed from two incidents in which traffic cameras caught a car registered to Chappell running red lights in Columbia. The pictures do not show whether Chappell was driving.

Chappell's son Moses described his father as a cautious, experienced driver. He said his father drove a city taxi, a tractor-trailer and school bus over decades. The longtime driver earned bonuses at work for his safe record, Moses Chappell said.

Before the crash, at about 6:30 a.m. Tuesday, Glenn Chappell and the aide were traveling east on Frederick Avenue to pick up their first student. The school bus hit a Ford Mustang and continued another block before crashing into the MTA bus.

Witnesses described mangled buses, trapped passengers and cries for help. One MTA passenger said she woke to find glass in her mouth and two bodies lying on her.

Those killed include the MTA bus driver, Ebonee Baker, 33, a mother of four children and three stepchildren; Cherry Yarborough, 51, a secretary at the state Department of Health and Mental Hygiene; Gerald Holloway, 51, a maintenance worker at Forest Haven Nursing and Rehabilitation; and Terrance Casey, 52, a former volunteer minister, husband and father.